PDK1 (3-Phosphoinositide-dependent kinase 1) is a serine/threonine kinase belonging to the AGC kinase super family. PDK1 was first identified as the upstream kinase responsible for activating protein kinase B/AKT in the presence of phosphoinositide lipids (PIP3). PDK1 activates AKT by phosphorylating a specific residue (threonine 308) located in the activation loop of this kinase. Subsequent research has shown that PDK1 is responsible for phosphorylating the activation-loop of many AGC kinases including p90 ribosomal S6 kinase (RSK), protein kinase C family members (PKC), p70 ribosomal S6 kinase (70S6K), and the serum and glucocorticoid-induced protein kinase (SGK). Thus, PDK1 is a central activator of multiple signaling pathways that are involved in cell proliferation, survival and control of apoptosis importantly, alterations in these signaling pathways are frequently observed in a variety of human cancers. For example, AKT is highly activated in a large percentage of common tumor types including melanoma, breast, lung, prostate and ovarian cancers. RSK levels are elevated in prostate cancers, and an RSK-specific inhibitor (SL0101) has recently been shown to inhibit the proliferation of multiple prostate cancer cell lines. Similarly, PKCε has been shown to play an important role in regulating apoptosis and promoting survival of glioma cells.
The human PDK1 gene encodes a 556 amino acid protein with an amino-terminal catalytic domain and a non-catalytic carboxy terminal containing a pleckstrin homology domain (PH). Recent studies suggest that PDK1 is a constitutively active kinase, and that PDK1 regulation occurs through the localization or conformational state of PDK1 target proteins. For example, the PH domain of PDK1 is required for the binding of PIP3 lipids produced by PI3kinase (PI3K). PDK1 binding of PIP3 lipids results in membrane co-localization with AKT, another PH domain containing protein. Once co-localized, PDK1 activates AKT by phosphorylating threonine-308. Alternatively, PDK1 can activate other AGC kinases independent of PIP3 lipids by binding directly to a conserved motif found on these targets. Because PDK1 regulates two distinct classes of downstream signaling substrates (PI3K-dependent and independent targets), inhibitors of this enzyme could have important therapeutic value in a variety of human cancers. For instance, PDK1 inhibitors could be efficacious in tumors in which the PI3K signaling pathway is upregulated due to activating mutations, amplification of PI3K itself or its upstream receptor tyrosine kinases, or deletion of PTEN, the phosphatase the counteracts PI3K activity. The finding that mice expressing half the normal amount of PTEN are protected from developing a wide range of tumors by reducing PDK1 expression levels supports this idea. Alternatively, PDK1 inhibitors could be useful in treating cancers driven by PIP3-independent PDK1 signaling pathways (e.g. K-ras or H-ras driven cancers).
Finally, the recent identification of PDK1 mutations (PDK1T354M, PDK1D527E) in human colorectal cancers suggests that inhibitors of this kinase may have therapeutic value by directly inhibiting either wild-type or mutant forms of this protein. See, Parsons et al., Nature 436, 792 (11 Aug. 2005) “Colorectal cancer: Mutations in a signaling pathway.”
In summary, PDK1 is a central activator of several signaling pathways that are frequently altered in human cancers making it an attractive target for therapeutic intervention.
U.S. Pat. No. 6,982,260 discloses quinazoline compounds for inhibition of cyclin-dependent kinases, and International Application PCT/IB2004/000091 discloses 2-aminopyridine substituted heterocycles as inhibitors for cellular proliferation.
This invention is directed to the discovery of novel compounds for PDK1 inhibition and use of these compounds to treat a variety of diseases or disorders involving cellular proliferation.